Nevada C-21D Refrigeration and Air Conditioning Maintenance Contractor Examination

Under NAC 624.380, which task is within Nevada C-21D Refrigeration and Air Conditioning Maintenance scope?

• AReplace the complete remote condenser assembly on a split refrigeration system
• BReplace an existing air handler with a larger-capacity unit
• CRedesign a rooftop unit to a different refrigerant and new coil circuiting
• DReplace a failed compressor, motor, relay, or coil on an existing air-conditioning unit

A C-21D contractor is asked to swap the entire outdoor remote condenser assembly on an existing split refrigeration rack. What is the correct scope decision?

• AProceed; any outdoor work is C-21D maintenance
• BDecline the complete assembly replacement; C-21D may replace condenser coils, fans, motor…
• CProceed if the new assembly has the same footprint
• DProceed if the owner signs a design-change waiver

Which existing-system repair is allowed under C-21D without altering system design?

• AReplace the indoor air handler and resize the supply duct
• BConvert a capillary-tube system to a custom-engineered EEV rack
• CInstall a new split system where none exists
• DReplace a leaking evaporator coil with a same-circuit, same-capacity coil

What are the four essential components of the vapor-compression refrigeration cycle on an existing C-21D unit?

• ACompressor, reversing valve, receiver, and accumulator
• BCompressor, condenser, metering device, and evaporator
• CCondenser, cooling tower, pump, and expansion tank
• DFilter-drier, sight glass, service valve, and crankcase heater

On an operating air-conditioning unit, where does refrigerant absorb heat from the conditioned air?

• AThe condenser coil
• BThe compressor discharge muffler
• CThe evaporator coil
• DThe liquid-line filter-drier

What is the primary function of the condenser on an existing air-cooled refrigeration unit?

• ATo boil liquid refrigerant and absorb space heat
• BTo reject heat so high-pressure vapor condenses to liquid
• CTo drop refrigerant pressure to evaporator saturation
• DTo store oil for the compressor crankcase

What does the compressor do to refrigerant vapor on an existing C-21D system?

• AIt lowers pressure so liquid can boil in the condenser
• BIt raises pressure and temperature so the condenser can reject heat
• CIt meters liquid into the evaporator at constant superheat
• DIt separates oil from liquid refrigerant in the liquid line

What is superheat on an operating evaporator?

• ASaturated condensing temperature minus liquid-line temperature
• BMeasured suction-line temperature minus saturated evaporating temperature at the suction…
• COutdoor dry-bulb minus condensing temperature
• DIndoor wet-bulb minus evaporator saturation temperature

What is liquid-line subcooling?

• ASuction-line temperature minus saturated suction temperature
• BDischarge-line temperature minus outdoor dry-bulb
• CEvaporator leaving-air temperature minus entering-air temperature
• DSaturated condensing temperature minus actual liquid-line temperature

What is the primary purpose of a liquid-line filter-drier on an existing refrigeration unit?

• ATo store extra liquid refrigerant for high-load periods
• BTo remove moisture, acid, and particulate from circulating refrigerant
• CTo raise suction pressure during a hot pull-down
• DTo replace the need for a vacuum after a repair

A property manager wants a C-21D contractor to add a second evaporator to an existing walk-in so the box can be split into two rooms. Why is that outside C-21D?

• AWalk-in evaporators can never be repaired under any C-21 license
• BAdding an evaporator and splitting the box alters the design of the existing system
• COnly sheet-metal (C-21C) contractors may work on walk-ins
• DUMC 2018 forbids any evaporator replacement

On a TXV system with a receiver, where is the receiver installed?

• AIn the suction line at the compressor inlet
• BIn the liquid line after the condenser and before the metering device
• CIn the discharge line between compressor and condenser
• DAcross the evaporator distributor tubes

Where is a suction-line accumulator installed, and what does it protect?

• AAfter the condenser, to store spare liquid for the TXV
• BIn the suction line, to keep liquid slugs from entering the compressor
• COn the discharge line, to strip oil from hot gas
• DAt the evaporator inlet, to distribute refrigerant to each circuit

Why is a crankcase heater used on an existing outdoor condensing unit?

• ATo increase condenser capacity on a 115°F day
• BTo defrost the evaporator during the off cycle
• CTo keep the TXV sensing bulb above 100°F
• DTo boil liquid that has migrated into the oil so the compressor does not start loaded wit…

Where is an oil separator installed on a commercial refrigeration unit, and what does it do?

• AIn the liquid line, to dry the refrigerant
• BIn the suction line, to store extra oil
• CIn the compressor discharge line, to return oil to the crankcase before the condenser
• DAt the TXV equalizer, to meter oil into the bulb

Compared with a reciprocating compressor, what is a typical service trait of a hermetic scroll compressor on an existing rooftop unit?

• AIt uses suction and discharge reed valves that are field-replaceable
• BIt compresses with orbiting wraps, is quieter, and is usually replaced as a sealed assemb…
• CIt requires a field-erected open drive and shaft seal on every unit
• DIt can be rebuilt in place by replacing only the piston rings

A liquid-line sight glass is normally installed where, and what does a clear glass after a long run mean?

• AOn the suction line; a clear glass means the compressor is flooding
• BAfter the filter-drier; a clear glass indicates a solid liquid column (moisture still nee…
• COn the discharge line; a clear glass means noncondensables
• DAt the oil return; a clear glass means the crankcase is empty

Why must suction-line piping on an existing system be insulated, while the liquid line is often left bare indoors?

• AUMC 2018 forbids insulating any liquid line
• BLiquid lines always operate above 200°F and need no covering
• CSuction vapor is below ambient dew point; insulation stops sweating and unwanted superhea…
• DInsulation on the suction line is only decorative

A suction-to-liquid heat exchanger on an existing rack is leaking. What is a C-21D-compliant repair?

• ADelete the heat exchanger and increase condenser face area
• BReplace the entire remote condenser assembly to eliminate the exchanger
• CReplace the heat exchanger with the same circuiting and capacity
• DConvert the rack from DX to a new chilled-water design

Under UMC 2018 Chapter 11, which copper tube is the correct material for field refrigerant piping on an existing system repair?

• AType M plumbing copper, as-received from a water-pipe rack
• BSeamless Type ACR copper complying with ASTM B280, cleaned and dehydrated
• CSoft medical-gas copper that has been stored open-ended on the truck
• DSteel EMT conduit used as a refrigerant sleeve and pressure boundary

While brazing a replacement liquid-line drier on an existing R-410A unit, what flow should be maintained through the tube?

• AOxygen to accelerate the braze and sterilize the tube
• BCompressed shop air so the joint cools faster
• CThe system’s remaining R-410A vapor to keep pressure on the joint
• DDry nitrogen at a low flow to displace oxygen and prevent internal scale

After a hermetic compressor burnout on an existing unit, what component change is required besides the compressor?

• AReuse the old drier if the sight glass was clear last season
• BReplace the liquid-line filter-drier (and usually add a suction drier) after flushing or…
• CReplace the complete remote condenser assembly as a matter of course
• DLeave the acid in the oil; POE will neutralize it

Under UMC 2018 refrigeration rules, a pressure-relief device protecting a vessel or condenser must be installed so that:

• AA service stop valve can isolate the relief for seasonal shutdown
• BNo stop valve is located between the relief device and the part of the system it protects
• CThe relief discharges into the occupied return-air plenum
• DThe relief is capped to keep dirt out

UMC 2018 requires refrigeration equipment to be identified. After a C-21D compressor and drier change, what must remain (or be restored) on the unit?

• AOnly the contractor’s cell number written on the compressor
• BA red tag that says the relief valve was capped
• CA nameplate or marking that identifies the refrigerant type and the system charge
• DNo marking; C-21D work is exempt from identification

A replacement condensate drain from an existing cooling coil must, under UMC 2018 Chapter 3, have a slope of not less than:

• A1/2 inch per foot so the trap always siphons
• BLevel, so water stands and seals the trap
• C2 inches per foot, the same as a sewage building drain
• D1/8 inch per foot (1 percent) toward the approved disposal point

What is the UMC 2018 minimum nominal size for an appliance condensate drain serving a cooling coil?

• A3/8 inch flexible vinyl
• B1/2 inch Type M copper only
• C3/4 inch, and the pipe must not reduce after the pan connection
• D2 inch ABS, regardless of coil size

A service valve on an existing condensing unit is a front-seating valve. What happens when the stem is turned all the way in (front-seated)?

• AThe port to the system is closed and the gauge port is open to the line leaving the valve
• BAll three ports are fully open (back-seated service position)
• CThe compressor is electrically locked out
• DThe relief valve is forced open

A replacement condenser fan motor on an existing 208/230-volt unit must be selected to match which of the following without changing system design?

• AVoltage, rotation, horsepower or wattage, speed (rpm), frame, and capacitor if used
• BOnly the color of the fan blade
• CA 460-volt motor on a 230-volt circuit if the amps are lower
• DAny higher-horsepower motor so the condenser “runs colder”

An existing air-cooled condenser is rejecting heat, but the liquid leaving the coil is only 2°F below saturation and the compressor discharge is abnormally hot. Which component problem best fits?

• AA TXV sensing bulb that has lost its charge
• BAn oversized suction accumulator
• CA severely fouled or air-starved condenser coil
• DA crankcase heater that is open

Noncondensable gas (air) left in an existing system after a sloppy repair will typically cause which running condition?

• ALow head pressure and a flooded compressor
• BZero superheat with a low evaporator load
• CA vacuum on the high side while the unit runs
• DHigh head pressure, high discharge temperature, and apparent excess subcooling that does…

UMC 2018 machinery-room emergency ventilation is sized by Q = 100 × √G, where Q is cfm and G is pounds of refrigerant in the largest system in the room. What exhaust rate is required for a 64-pound charge?

• A400 cfm
• B640 cfm
• C800 cfm
• D6,400 cfm

An existing indoor fan-coil’s primary condensate drain can overflow onto a finished ceiling. Besides repairing the primary drain, what UMC 2018 protection must remain in service?

• AA 2-inch open standpipe into the electrical closet
• BA plugged secondary so the pan holds extra water
• CAn auxiliary drain pan with a separate observed drain, or a water-level device that shuts…
• DNo extra protection; C-21D work is exempt

A C-21D changeout of a POE-oil R-410A compressor has the system open for two hours on a humid day. What is the correct oil and evacuation concern?

• APOE rejects water, so a 5-minute vacuum is enough
• BAdd mineral oil to dilute any moisture
• CCharge first, then vacuum the high side only
• DPOE is highly hygroscopic; minimize open time, replace the drier, and pull a deep vacuum…

What is the job of the metering device on an existing refrigeration unit?

• ATo raise vapor pressure so the condenser can reject heat
• BTo drop liquid pressure and feed a low-pressure mixture into the evaporator
• CTo store spare oil for the compressor
• DTo convert the system from cooling to heating

How does a thermostatic expansion valve (TXV) control refrigerant feed?

• AIt holds a constant evaporator pressure regardless of load
• BIt modulates to hold a relatively constant evaporator superheat
• CIt is a fixed hole whose flow never changes
• DIt opens fully whenever the compressor contactor is energized

On a fixed-orifice (piston) air conditioner, which measurement is used to set or verify charge?

• ALiquid subcooling only, ignoring indoor wet-bulb
• BTotal superheat compared with the manufacturer’s charging chart
• CDischarge-line temperature alone
• DCompressor RLA alone

An R-410A unit shows 118.9 psig suction and a 52°F suction-line temperature at the evaporator outlet. What is the evaporator superheat?

• A8°F
• B10°F
• C12°F
• D18°F

An R-410A unit shows 364.1 psig liquid-line pressure and a 98°F liquid-line temperature. What is the subcooling?

• A8°F
• B10°F
• C12°F
• D20°F

An R-22 cooler shows 68.6 psig suction and a 54°F suction-line temperature. What is the superheat?

• A8°F
• B10°F
• C14°F
• D22°F

An R-22 condensing unit shows 226.4 psig liquid pressure and a 100°F liquid-line temperature. What is the subcooling?

• A6°F
• B10°F
• C15°F
• D26°F

A running system has high superheat and low subcooling, with low suction and low head. What is the most likely charge problem?

• ARefrigerant overcharge
• BA restricted liquid-line drier with a full receiver
• CA TXV that is flooding the evaporator
• DRefrigerant undercharge (or a large leak)

Where should a TXV sensing bulb be clamped on a horizontal suction line?

• AOn the bottom of the pipe, in the oil stream
• BAt about the 10 o’clock or 2 o’clock position, tight and insulated
• COn the compressor discharge muffler
• DLoosely hung in the airstream so it reads room temperature

When must a TXV have an external equalizer, and where is that tube connected?

• AOn any evaporator with significant distributor or coil pressure drop; tap the suction lin…
• BOnly on capillary-tube systems; tap the liquid line
• COnly on water-cooled condensers; tap the drain pan
• DNever; external equalizers are obsolete

A TXV hunting (superheat swinging several degrees) on an existing coil is most often corrected by which maintenance action?

• AOpening the adjustment stem several turns at once to flood the coil
• BReplacing the complete remote condenser assembly
• CRemoving the external equalizer
• DChecking bulb contact and insulation, and making only small superheat-spring adjustments

A TXV whose power element has lost its charge will typically produce which symptoms?

• AHigh superheat, starved evaporator, low suction, and a coil that is only partly active
• BZero superheat and liquid slugging
• CHigh suction and a flooded sight glass with low superheat
• DA compressor that will not stop on the thermostat